Stratigraphy & Correlation


Rock Record:

• Three major ways of

subdividing the geologic

record:



Rock Units (lithology):

• bodies of rock defined by

their distinctive lithologic

features



Rock Units (lithology):

• must be wide spread.

= mapable.



Divisions of Rock Units:

Group

Formation - fundamental unit

MemberBed - informal unit


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Rock Unit Names are based on:

1) Geographic location(where first described)

and

2) Rock type (lithology)



Rock Unit Names: for example

Blowing Rock Gneiss

Erwin Sandstone

Grand Father Mountain Formation(mixed

lithology)



Characteristics of Rock Unit:

• primarily an environmental indicator. • but environments change position through time.




therefore, boundaries of rock units

do not correspond to time units !!!




• boundaries of rock units

do not correspond to time!!



2. Time Units: (chronology)

• intervals of time

• independent of associated rocks (durations in millions of year).



Division of Time Units:

• Eon Era Period - fundamental unit Epoch Age



Characteristics of Time Units:

• not equal subdivisions (e.g. not equal divisions of say, 10 million yrs)

• may include more than

one rock type



Characteristics of Time Units:



time interval

3. Time-Rock Units:

• All of the rocks deposited

during a particular interval of time.



Time-Rock Units:



Time Time-RockEon (Eonothem) Era (Erathem) Period System Epoch Series Age Stage

All of the rocks deposited during theCretaceous Period . . .

Belong to the Time-Rock Unit of theCretaceous System.



Review: ways to divide the rock record

Rock Units - lithology - can vary in age

Time Units - unequal divisions of time, will have variable rock types

Time-Rock Units - all of the rocksdeposited during a given interval of time



Correlation:

• Establishment of an equivalence between two rock units.



1. Lithologic correlation:

• determine whether two rock

bodies are (or were) part of

the same rock body.



How? • physically trace the outcrop





How? distinctive lithologic identity Claystone Limestone

Limestone Shale

Shale Sandstone

Sandstone Conglomerate

How? position in a stratigraphic sequence



How? geophysical properties



How? geophysical properties (e.g., radioactivity)



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How? geophysical properties (e.g., radioactivity)



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2. Time correlation:

• Process of determining whether

two rock bodies were deposited

at the same time.



Time correlation: How?

• Radiometric dating (e.g. 14C)

• marker beds (e.g. volcanic ash bed)

• paleomagnetic reversals



3. Biological Correlation:(Based on the Principle of Fossil Succession)

• Rocks with the same fossil assemblages were deposited during the same interval in geologic time.



Stratigraphy & Correlation

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